Known in the art are methods for preparing graft copolymers of cellulose with monovinyl monomers containing ionic groups or non-ionic groups capable of being converted to ionic ones by way of a free-radical graft polymerization, on cellulose, of said vinyl monomers in the presence of a free-radical type initiator.
However, during graft-polymerization, onto cellulose, of monovinyl monomers such as acrylic acid or methacrylic acid, or in a polymer-analogous conversion of said non-ionic groups to ionic ones there occurs a considerable swelling of the resulting copolymers. This phenomenon does not make it possible to obtain the desired product which would be uniform in its composition. It also results in impaired working properties during the ion exchange process (i.e. hinders multiple use of fibrous ionites in processes of sorption and desorption), the formation of adhesive bonds between fibers, increased brittleness of fibers thus precluding the possibility of textile processing the fibers to woven fabrics, non-woven materials and other textile goods.
Also known in the art is a method for preparing graft copolymers of cellulose with vinyl monomers containing non-ionic groups capable of being converted to cation exchange groups by way of a radical graft polymerization, onto cellulose, of said monovinyl monomers in the presence of free-radical type initiators, followed by the treatment (for the purpose of converting non-ionic groups to ionic ones) of the resulting graft-copolymers with a 2.5-10 M solution of an alkali at a temperature within the range of from 100.degree. to 130.degree. C. for a period of from 10 to 30 minutes and washing said copolymers with alcohols to remove the excessive alkali.
Said process makes it possible to avoid an excessive swelling of graft copolymers of cellulose during a polymer-analogous conversion of non-ionic groups to ionic ones and during an ion exchange process, as well as to obtain the desired products with a uniform composition and a high sorption power. However, the products prepared by this method comprise segregated clots formed by short fibers adhering to each other. Such products are not suitable for further textile processing.
Also known in the art is a method for preparing modified graft copolymers of cellulose with monovinyl monomers containing ionic groups. The method comprises treatment of cellulose with a modifying (cross-linking) agent such as dimethylolethyleneurea or formaldehyde in the presence of an acidic catalyst, followed by xanthation of the modified cellulose and a radical graft polymerization, onto the modified cellulose, of monovinyl monomers containing ionic groups in the presence of free-radical type initiators.
This method, however, is a multi-staged one and gives rather brittle products. The modification (cross-linking) by means of, for example, dimethylolethyleneurea or formaldehyde results in the formation of short bridges between macromolecules of cellulose and, consequently, in impaired relaxation properties of the polymer. Furthermore, brittleness of the resulting graft copolymers is due to a lowered molecular mass of cellulose associated with acidic hydrolysis thereof occurring under the effect of said acidic catalyst. An increased brittleness of the fibrous materials prepared by this prior art method makes these materials unsuitable for further textile processing to woven fabrics, non-woven materials and other textile products.
It is an object of the present invention to overcome the above-mentioned disadvantages inherent in the prior art methods.
The present invention is directed to the provision, in a method of preparing modified graft copolymers of cellulose with monovinyl monomers containing ionic groups or non-ionic groups capable of being converted to ionic ones, of a modifying agent and conditions of radical graft polymerization and modification which make it possible to simplify the process technology and equipment and obtain the desired products with a high exchange capacity, an optimal degree of swelling and capability of being processed in textile fabrics, non-woven materials and other textile products.